Arrows that are used in the sport of archery may be formed of a wide variety of materials, including wood, aluminum or other metals, and carbon fiber materials. The aluminum and carbon fiber arrows are usually formed in a hollow tubular configuration, with a nock attached to the rearward end of the shaft and various types of points attached to the forward end of the shaft.
In the construction of a complete arrow, a shaft is first cut to the desired length and then an attachment structure may be mounted on the forward and rearward ends to connect the desired point and nock into position on the ends of the shaft. Although the point and nock may be permanently mounted to the shaft, it has become common to provide an attachment structure for the shaft which permits replacement of the point with a variety of structures, including broadheads, target points and the like.
Currently, metal inserts are provided for attaching a point or nock to the ends of an arrow shaft. Commonly, the insert is glued into the interior of the shaft, and is provided with an interiorly threaded bore for connection of a point or nock. One critical problem in the attachment of inserts on hollow shafts is in the mounting of the insert in coaxial alignment with the shaft. Because of spaces provided for glue between the metal insert and shaft, there is a loose fit between the insert and shaft, which permits the possibility of misalignment of the insert with the shaft during the curing of the glue which holds the insert in position.
One solution to this problem is provided in U.S. Pat. No. 4,943,067 to Thomas A. Saunders, which calls for an arrow insert having a pair of annular alignment rings with outer diameter slightly larger than the inside diameter of the arrow shaft. In this way, as the insert is pushed into the arrow shaft, the alignment rings will assure substantial coaxial alignment of the insert with the shaft because of direct continuous contact of the annular rings with the interior of the shaft.
While the arrow insert of the '067 patent works well for hollow metal shafts, newer shafts are being formed in increasingly smaller diameters and with increasingly lighter weight materials, including carbon fiber and the like. These new materials are typically weaker in radial tensile strength than prior art heavier weight materials, and therefore can easily crack if an insert applies too great of an outward pressure by virtue of alignment rings on the insert. In addition, as the shaft diameter decreases, it is more difficult to provide a central threaded bore which will receive the common arrow point threaded shaft, for easy replacement of points.